1. Field of the Invention
The present invention relates to a power conversion device that includes semiconductor switches connected in series.
2. Description of the Related Art
Turning a switching element on and off in a power conversion device causes abrupt changes in current and voltage, which may generate noise. The noise may adversely affect other control circuits in the device. Japanese Unexamined Patent Application Publication No. 2007-13916 describes a method to reduce the level of noise of this type. In the method described in Japanese Unexamined Patent Application Publication No. 2007-13916, a rising edge of a PWM signal applied to the switching element is shaped into a substantially sine waveform when the switching element is under switching control. This changes the waveform of a current flowing through a load to have a smoother slope at the rising edge and makes the current change moderate, thus avoiding noise generation resulting from abrupt changes in current and voltage.
Recently, switching elements using compound semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), have been put into practical use. This enables power conversion devices to operate at high frequencies, and resulting miniaturization of passive components is encouraging attempts to downsize such power conversion devices. However, in Japanese Unexamined Patent Application Publication No. 2007-13916, shaping the rising edge of a PWM signal into a substantially sine waveform increases the dead time of a switching element, which decreases the switching frequency. In short, it is difficult to increase the switching frequency using the method described in Japanese Unexamined Patent Application Publication No. 2007-13916.